Compensator for induced magnetic fields



Dec. 14, 1954 FIG. 2

COMPENSATOR FOR INDUCED MAGNETIC FIELDS w. c. ANDERSON 2,697,186

Filed July 31, 1944 44 VL I W/L ME 6. ANDERSON United States Patent Ofltice 2,697,186 Patented Dec. 14, 1954 COMPENSATOR FOR INDUCED MAGNETIC FIELDS Wilmer C. Anderson, Douglaston, N. Y., assignor to the United States of America as represented by the Secretary of the Navy Application July 31, 1944, Serial No. 547,449 1 Claim. (Cl. 317-123) an opposing field obviously cannot be efiected by a simple procedure in accordance with which the fields due to compensated without necessitating previous the orientation of each contributing member.

There is knowledge of ferromagnetic to each of the coils. For a better understanding of the invention, reference is made to the accompanying drawings in which: Fig. 1 is a diagram showing a reference system by means of which the orientation of the aircraft in relation means of the arrow H, ence axes and the direction of the earths are designated X, Y and Z, respectively.

The total induced magnetic field of the aircraft, due to a random distribution of magnetic members, may be reproduced by means of three orthogonal ferromagnetic virtual bars of proper dimensionsv Conveniently, these virtual bars may be chosen in such fashion that they are p rallel respectively to the x, y and z axes, these b rs being designated the transverse, longitudinal and vertical bars. Each of these bars produces a field in the direction of the axis to whi h it is parallel, and because the bars do are they necessarily ill) each may also produce a field in the direction of the other two axes. For example, it is evident For convenience, the fields produced by the bars in the direction of the axes along which they are oriented may be designated TT, VV, where the first letter indicates the direct1on of the causing the field and the second letter indicates the direction of the field ds for a transverse bar ducing a transverse field, etc. Fields produced by bars along other axes may be designated TL, VT, as that used above.

causing the field and the earth components are indicated in Fig. 1

The total induced field E1 is the vector sum of these nine components and may be expressed in the following manner:

(TT cos X-LT cos Y-VT cos Z)t' (TL cos X-LL cos Y-VL cos Z) 7' (TV cos X-LV cos Y-VVcos Z)k to achieve compensation, means must be provided for producing opposing fields proportional in magnitude to the magnitude of the earths magnetic field H multiof the aircraft in respect to the earths field.

e present invention provides a system whereby quantities proportional to each term of the above equation may be produced to compensate the total induced magnetic field of the aircraft. Referring to Fig. 2, three magnetometers 10, 12 and 14 are arranged to measure the components of the earths magnetic field along the x, y and z axes, respectively.

chosen direction, they may conveniently be of the type disclosed in copending application Serial No. 516,612, filed January 1, 1944, Unbalanced Magnetometers, Otto H. Schmitt, and now Patent Number 2,560,132, in acset of unbalanced magnetometer produce magnetic rietometer is proportional to (H cos X), that of magnetometer--12 to (-H cos 'Y)-,--and that of magnetometer 14 to (H cos Z). Accordingly, through appropriate settings of attentuators 34, 40 and 46, and reversing switches 16, 22 and 28, the magnitudes of constants T1 VT, and, LT may be adjusted so that-all terms due to fields in the direction of the -x 'axis will be compensated.

In a similar fashion, adjustmentsrof attentuators 38, 44 and 50 and the associated reversing switches 20, 26 and 32 vary constants TL, VL, and LL and permit corn-1 pensation of all terms due to fields in the direction of the y axisyand adjustments of the remaining attentuators each of which includes a coil and a core, said magnetometers being positioned in said aircraft on mutually perpendicular-axes, said magnetometers measuring components of the earths magnetic field along said mutually perpendicular axes and producing voltages proportional 5 to the measured components, a compensating co' mounted on the same axis with each of said magnetometers, and separate circuit means connecting the output from each of said magnetometers to each of said coils, 'each of said circuit means including a reversing switch and attenuator means.

References Cited in the tile of this patent 36, 42 and 48 and the reversing switchesassociated therewith permit variation of constants TV, VV and LV UNITED STATES PATENTS andcompensation of terms due to fields in the direction Number Name Date of the z axis Thus it will be seenthat, through appro- 41,839 Gisborne Mar. 8, 1864 priate adjustment of thenine reversing switches and the 1,596,639 Vion Aug. 17, 1926 nine attentuators, the above equation may be satisfied 1,672,328 Loth June 5, 1928 for any distribution of magnetic members producing the 1,892,826 Bettison et al. J an. 3, 1933 total induced magnetic field of the aircraft. 2,252,059 Barth Aug. 12, 1941 In the use of the device, all of the attenuators are 2,324,718 Noxon July 20, 1943 initially set in such fashion that no current flows in com- 2,412,617 Jenkins Dec. 17 1946 pensating coils 52, 54 and 56. Then as the aircraft 2,427,666 Felchet a1. Sept. 23, 1947 maneuvers, adjustments of the attenuators are made until 2,438,964 Cunningham et-al Apr. 6, 1948 the total induced field as recorded by suitable measuring instruments is reduced to a minimum, the reversing FOREIGN PATENTS switches tigirlig use'dhwhere necessary to provide corn- Number country Date pensating e so t e proper .po arity.

What is claimed is: t. germany 8 ii Apparatus for conpe'nsat-ing a nftagietically sensitive ermany instrument mounte in an aircra t or t e magnetic field induced in the ferromagnetic members in said air- V OTHER REFERENCES craft, said apparatus comprising three magnetometers Electricity and Magnetism, by S. G. Starling, Longmans, Green and Co., Ltd., London; 1929; pages -50. 

